1. Field of the Invention
The present invention relates to a heat exchanger in which high-temperature fluid passages and low-temperature fluid passages are circumferentially alternately formed.
2. Description of the Related Art
There are conventionally known heat exchangers including high-temperature fluid passages and low-temperature fluid passages defined in an annular space, which are described in Japanese Patent Application Laid-open Nos. 57-2982, 57-2983 and 56-149583.
There is also a conventionally known heat exchanger described in Japanese Patent Application Laid-open No. 58-40116, in which a folding plate blank composed of a plurality of first heat transfer plates and a plurality of second heat transfer plates alternately continuously formed to each other through first and second folding lines are folded into a zigzag fashion at the first and second folding lines, a gap between the adjacent first folding lines being closed by bonding of the first folding lines and a first end plate, a gap between the adjacent second folding lines being closed by bonding of the second folding line and a second end plate, and high-temperature fluid passages and low-temperature fluid passages are alternately formed between the adjacent first and second heat transfer plates.
The heat exchangers described in Japanese Patent Application Laid-open Nos. 57-2982 and 57-2983 have a problem that the folding lines in the folding plate blank constituting the heat transfer plates are complicated and for this reason, a great deal of labor is required for a folding operation to increase a working cost. Another problem is that inlets of the high-temperature and low-temperature fluid passages open in a direction perpendicular to axes (i.e., radially) and hence, the flow of the fluid is abruptly bent at such open portions to produce a pressure loss. The heat exchangers described in Japanese Patent Application Laid-open No. 56-149583 has a problem that the direction of flow paths at the inlets and outlets is perpendicular to the direction of flow paths in the high-temperature or low-temperature fluid passages and hence, the flow of the fluid is abruptly bent at such perpendicular portion to produce a pressure loss. Further, in this heat exchanger, ducts are connected to the inlets and outlets permitting the fluid to flow radially. Therefore, there is a problem that it is difficult to form the ducts along an axial direction of the heat exchanger, resulting in an increase in radial dimension of the heat exchanger.
The heat exchanger described in Japanese Patent Application Laid-open No. 58-40116 has a problem that the sectional area of the flow path is constricted to about one half at the outlets and inlets of the high-temperature and low-temperature fluid passages, resulting in a great pressure loss produced at such portion. Moreover, the heat exchanger also has another problem that the outlets and inlets are formed by folding the folding plate blank and hence, the folding lines are complicated, resulting in a great deal of labor required for the folding operation to increase the manufacture cost. A further problem is that if the difference in pressure between the high-temperature or low-temperature fluid passages is large, a spacer is inserted between the first and second heat transfer plates to maintain the strength, resulting in increases in number of parts and in number of assembling steps by such a spacer. Further, the fluid outlet and inlet formed adjacent each other are intricate with each other and hence, if an attempt is made to partition the outlet and inlet by a partition member, the structure of the partition member becomes complicated, and the area of the bond area such as the brazed area is increased, resulting in a possibility of a fluid leakage being produced.